Controlling delivery of polymer material in a sequential injection molding process

ABSTRACT

Method and apparatus for controlling the delivery of polymer material in a sequential injection molding process. In one embodiment, the method provides: delivering a first shot of a first material simultaneously to a plurality of mold cavities; independently sensing for each cavity a property that is indicative of a volume or flow of material that is delivered to the corresponding cavity during the step of delivering the first shot; independently stopping the step of delivering the first shot to one or more cavities according to a program that uses as a variable a signal indicative of the property sensed for the corresponding cavity during delivery of the first shot; and delivering a second shot of a second material simultaneously to the cavities subsequent to the step of stopping the step of delivering the first shot.

FIELD OF THE INVENTION

The present invention relates to controlling one or more of a volume orflow of a first shot of polymer material delivered to a mold in asequential injection molding process. In a particular embodiment, theinvention relates to controlling the simultaneous injection of a firstshot of polymer material to a plurality of cavities in a sequentialprocess.

BACKGROUND OF THE INVENTION

Injection molding processes for performing sequential shots of differentpolymer materials are well known. To accomplish such processes,injection molding apparati have been developed using hotrunner systemsthat are designed to deliver sequential shots of polymer material bothto a single cavity and to a plurality of cavities. In multi-cavityapplications, shots are intended to be delivered at the same time in thesame amounts and at the same rates of flow by controlling the length andconfiguration of the hotrunner flow channels and the temperature ofvarious portions of the hotrunner and the injection nozzles and the moldcavity itself. However, in practice, it is very difficult to achievesuch uniform delivery to multiple cavities.

When shots of plastic materials are delivered in sequence to even asingle cavity, it can be difficult to obtain consistency in the preciseamount of the shots from one cycle to the next. When shots are routedthrough multiple flow channels in a hotrunner leading to multiplecavities, it is even more difficult to maintain precise control over thepressure within any given channel or injection nozzle or mold cavity andthus the rate and/or volume of material flow to any particular one ofthe plurality of cavities will vary. When a single source of polymermaterial injection is used to effect flow through all channel paths toeach mold cavity, pressure will vary between the flow paths even atpoints within different channels that are located the same distance(path length) from the source of injection. Performing two or more shotsof material one after the other further increases the degree ofdifference of volume of polymer material that is delivered to differentcavities in each shot. Still further, changes in the polymer material(s)over time (e.g., different batches, sources, temperatures, moisturecontent) can alter the flow characteristics even for a specifichotrunner/cavity path.

Prior systems describing typical sequences of injecting sequential shotsof first, second and/or third shots of polymer materials into moldcavities and the apparati used to effect such multi-cavity injection areset forth in U.S. Pat. Nos. 4,550,043; 4,609,516; 4,710,118; 4,781,954;4,950,143; 4,990,301; 4,923,723; and 5,098,274, the disclosures of allof which are incorporated herein by reference as if fully set forthherein.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the invention there is provided amethod of delivering multiple shots of material to a plurality of moldcavities, the method comprising:

delivering a first shot of a first material simultaneously to aplurality of mold cavities;

independently sensing for each cavity a property that is indicative of avolume or flow of material that is delivered to the corresponding cavityduring the step of delivering the first shot;

independently stopping the step of delivering the first shot to one ormore cavities according to a program that uses as a variable a signalthat is indicative of the property sensed for the corresponding cavityduring delivery of the first shot; and

delivering a second shot of a second material simultaneously to thecavities subsequent to the step of stopping the step of delivering thefirst shot.

Each cavity can have a corresponding nozzle fluidly communicating withthe cavity and having a first bore for delivery of the first shot, thenozzle having a valve pin adapted to open and close the first bore, andthe step of independently stopping the first shot comprising closing thefirst bore.

In one or more embodiments, the step of delivering the second shot maycomprise delivering the second shot subsequent to stopping delivery ofthe first shot to all of the plurality of cavities. The step ofdelivering the first shot may comprise delivering the first material toall of the plurality of cavities from a single source of injection. Thestep of delivering the second shot may comprise delivering the secondmaterial to each cavity from a separate source of injection.

In one or more embodiments, the step of independently sensing maycomprise sensing a property of the first material at one or moreselected locations of flow, wherein the program uses a signal indicativeof the sensed property at the one or more locations to either calculateflow rate or fill volume of the first material or to compare the signalor a value calculated from the signal to a target value. The targetvalue may be a minimum value or a range of values. In one embodiment,the property of the first material is sensed at a single location offlow. In another embodiment the property of the first material is sensedat two locations of flow.

The step of independently sensing preferably comprises sensing one ormore of a pressure, a temperature, a flow rate, an optical property, afill volume or level of the first material into or in the cavity.

In another aspect of the invention, there is provided an injectionmolding apparatus comprising:

a plurality of mold cavities, each cavity communicating with acorresponding nozzle that delivers two or more materials to itscorresponding mold cavity;

each nozzle having a corresponding valve and communicating with a sourceof pressurized feed of the two or more materials;

a drive mechanism that drives one or the other or both of the sources ofpressurized feed and each valve for each nozzle, the drive mechanismstarting and stopping flow of each of the two or more materials in apredetermined sequence through the nozzles;

a controller interconnected to the drive mechanism, the controllerincluding instructions for directing the drive mechanism to operate todeliver at least a first shot of a first material and a second shot of asecond material after the first shot;

one or more sensors associated with each cavity adapted to sense aproperty indicative of a volume or flow of the first material that isdelivered to the corresponding cavity; and

the controller being adapted to receive signals from the sensors andincluding a program having instructions for using the received signalsas a variable to enable and stop the flow of the first shot of the firstmaterial to each cavity to achieve a predetermined volume of the firstmaterial in each cavity.

Each nozzle can have first and second bores for delivering the first andsecond materials respectively to the corresponding cavity, each valveincluding a pin that reciprocates between open and closed positions. Inthe closed position both the first and second bores are closed; the openpositions include at least first and second open positions wherein inthe first position the first bore is open and the second bore is closed,and in the second position the first bore is closed and the second boreis open, the program using the first signal as a variable to direct thepin to move between positions.

In various embodiments, one or more sensors are disposed at one or morelocations of the flow of the first material in or into eachcorresponding cavity. The program includes instructions that use thesignal from a sensor that is indicative of the sensed property of theone or more locations to either calculate flow rate or fill volume ofthe first material or to compare the signal or a value calculated fromthe signal to a target value. The one or more locations may be within abore of the nozzle or within a corresponding cavity or within themanifold/hotrunner. In one embodiment, a single sensor is disposed atone location for each cavity. In another embodiment, at least twosensors are disposed at two locations for each cavity.

The sensor typically comprises at least one of a pressure sensor, atemperature sensor, a flow meter, an optical sensor, a fill volume orlocation sensor, or the like.

In another embodiment, a method is provided for delivering multipleshots of material to a mold cavity, the method including the steps of:

delivering a first shot of a first material to the mold cavity;

sensing a property that is indicative of a volume or flow of firstmaterial that is delivered to the cavity during the step of deliveringthe first shot;

stopping the step of delivering the first shot to the cavity accordingto a program that uses as a variable a signal indicative of the propertysensed during delivery of the first shot; and

delivering a second shot of a second material to the cavity subsequentto the step of stopping the step of delivering the first shot.

In this embodiment, the method may be used to control delivery of thefirst shot while forming a plurality of articles in the mold cavity,i.e., during two or more sequential molding cycles. The method alsoenables providing at least a predetermined amount of a first shot oversequential molding cycles when there has been a change in one or moreproperties of the first material, such as an alteration in intrinsicviscosity, moisture content, molecular weight, temperature, or othervariations in the material.

In one or more embodiments, the valve pins are individually controlledto determine a completion of the first shot in the corresponding cavity.In other embodiments, the valve pins are used to determine anintermediate point during the filling of the corresponding cavity withthe first material.

In various embodiments, the valve pins, which previously were only usedby all opening at the start of a cycle and all closing at the end of aninjection hold time, can now perform the intermediate step ofindividually closing to stop flow to certain cavities under thedirection of a controller (e.g., microprocessor).

In one embodiment, a three-position valve pin is provided movable to anintermediate position, wherein the first shot material flow is stopped,but other material(s) are not blocked. While the other materials areflowing, all valve pins to the cavities would be in the intermediateposition.

In another embodiment, a two-position valve pin is provided. In thisembodiment, by stopping the flow of the first shot to a correspondingcavity, all flow to the cavity is blocked. The valve pin then needs tobe reopened before any of the material can enter the correspondingcavity.

In one embodiment, a two-material (2M) three-layer (3L) article isformed. After completion of the first shot, the valve pins would eitheropen (two-position valve) or stay in the intermediate position(three-position valve) for the second material to be injected. After thesecond material is injected, all valve pins would open for a small lastshot of the first material to clear the gate of the second material(enclosing the second material as an interior layer). This embodimentwould not utilize any shooting pots.

In another embodiment, a two-material (2M) five-layer (5L) article isformed. After completing the first shot, the valve pins would eitheropen (two-position valve) or stay in the intermediate position(three-position valve) for the second material to be injected. Afterthis, all valve pins would open fully while the remainder of the cavityis filled and packed. Shooting pots may or may not be used for thesecond material.

In another embodiment, a three-material (3M) five-layer (5L) article isformed. After completing the first shot, the valve pins would eitheropen (two-position valve) or stay in the intermediate position(three-position valve) for the second material to be injected. The valvepins would stay in this position while the third material is injected.Shooting pots may or may not be used for the second and third shots.

In some embodiments, it may be determined that several cavities sharesubstantially the same filling rate or volume and can be combined on thesame control circuit, thus simplifying the apparatus by reducing thenumber of sensors and valve control circuits needed.

One method of detecting the flow rate in a cavity is from one or moresensors located in a part of the cavity which will be occupied by thefirst shot, i.e., detecting the presence of the melt at that location.These sensors can be exposed to the melt, or disposed just below themolding surface. For example, optical sensors, such as fiber optic, canbe incorporated into the molding surface. Temperature sensors or sensorsof another type can be positioned at the surface or just below themolding surface.

In one embodiment, two sensors are located at different points along thedirection of the flow path of the first shot in the cavity. The timeperiod for flow between the sensors would be a direct measurement of theflow rate. Alternatively, using a single sensor per cavity, the flowrate could be calculated based on the start time of injection.

In select embodiments, the flow rate may be detected based ontemperature sensors located in a high shear area, such as at the gate.

In another embodiment, the controller may be operatively disposed tocontrol a first shot injection unit, directing the unit to slow downdelivery as the valve pins are closing. Furthermore, it may control theinjection unit to stop the flow when all valve pins are closed. Thecontroller may also generate a signal to open the valve pins.

The processes and apparati of various embodiments may be used in themanufacture of multilayer plastic articles such as preforms, bottles andother packaging articles. The polymer materials injected typicallycomprise one or more structural polymers and/or optionally one or morespecific functional polymers, for example high temperature, gas barrieror scavenging materials. The structural material is typically injectedas the first shot and then a gas barrier, scavenging or recycled (e.g.,reprocessed scrap or post consumer) material is injected as the secondshot. As a third shot, either a structural, specific functional, orrecycled material may be used.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further advantages of the invention may be betterunderstood by referring to the following description in conjunction withthe accompanying drawings in which:

FIG. 1 is a schematic view of a multi-cavity mold system where each moldcavity fluidly communicates via a hotrunner channel system with a commonsource of pressurized fluid material, each mold cavity filling at adifferent rate during a single injection cycle;

FIG. 2 is a schematic view of a multi-cavity mold system where thedelivery of material to each cavity is controlled via a valve/valve pinthe operation of which is controlled by a signal received from a sensormonitoring the flow of material into each cavity;

FIG. 3 is a schematic view of a multi-cavity injection mold system,showing a single cavity, where three different materials arecontrollably injected into each cavity;

FIG. 4 is schematic side view of two separate cavities that are fed by acommon source of polymer material injection, showing the progress oftravel of injected polymer material in each cavity during the course ofa single shot of material;

FIG. 5A is a schematic side cross sectional view of a three-layerpreform and FIG. 5B is an enlarged fragmentary sectional view of aportion of the multilayer wall of the preform;

FIG. 6A is a schematic side cross sectional view of a blown bottle madefrom the preform of FIG. 5A and FIG. 6B is an enlarged fragmentarysectional view of a portion of the wall of the bottle showing morespecifically the multilayer wall of the bottle;

FIGS. 7A-7D are schematic side cross-sectional views of a single moldcavity showing the progress of travel of polymer material flow into thecavity as a result of first, second and third shots of polymer materialsthat are sequentially injected to form a five-layer article;

FIGS. 8A-8C are side, cross-sectional views of a three-positionactuator/valve pin and associated three bore nozzle usable in selectembodiments of the invention.

DETAILED DESCRIPTION

FIG. 1 shows a mold system having a multiplicity of essentiallyidentically shaped cavities 14 a-14 i that are fed by a single source ofpolymer material injection 10. The system shown in FIG. 1 does notinclude shooting or metering pots to assist in controlling the amount orpressure of material flow to each cavity but rather uses only the singlesource 10 of injection that provides all of the pressure by which theinjected polymer material is forced to flow through all of the variousand different manifold channels 12 a-12 c and into all of the multiplenumber of cavities 14 a-14 i. As shown, the forwardmost progress oftravel of polymer material into each cavity 14 a-14 i is different foreach cavity, the top or leading edge level of polymer material withineach cavity varying in distance either above or below travel line 16 asshown in FIG. 1. These differences in rate and volume of materialfilling of identically shaped cavities arises out of minor differencesin the size, shape, length and temperature of the path of channel travelfrom the source 10 through the channels 12 a-12 c to the separatecavities, as well as minor differences in the cavities 14 a-14 ithemselves. Such differences in flow rate can be caused by very smalldifferences between channel paths or cavities (e.g. tenths ofmillimeters in length or diameter or fractions of a degree intemperature) but such differences still result in the differences infill rate among different cavities as shown in FIG. 1. Even smalldifferences in fill rate can have a significant effect on the structureof the molded articles, e.g. the location of an interior barrier layerin a multilayer preform.

Methods and apparati for carrying out sequential first, second and thirdshots of materials arise in a variety of contexts pertinent to thepresent invention and are described by way of the following examples. Atypical embodiment of a three-material (3M), five-layer (5L) moldedarticle is illustrated in FIGS. 5A, 5B, 6A and 6B. A multilayeredpreform 110 manufactured by an injection molding process is shown inFIG. 5A. The multilayered preform 110 has a central core layer 130,intermediate interior layers 136 and 138 on opposite sides of the corelayer, and exterior inner 132 and outer 134 layers. The bottle 210 shownin FIG. 6A is made from preform 110 by a blow molding process. Similarto the preform the wall of the bottle has a core layer 230, exteriorinner and outer layers 232, 234 and interior intermediate inner andouter layers 236, 238. In a typical embodiment of a multilayer preformand/or bottle, the core 230 and exterior layers, 232, 234 of the FIG. 6Bbottle and/or the preform layers 130, 132, 134, FIG. 5B, are comprisedof a structural polymer. The intermediate layers 236, 238 or 136, 138is/are typically comprised of another polymer such as a barrier orscavenging polymer as is well known in the art. Injecting the firststructural layer material in a precisely desired amount to each one of amultitude of mold cavities is important to achieving a proper layeringwithin the cavities of a second injected material relative to the firstinjected material as shown schematically in FIGS. 7A-7D. Typicalexamples of multilayered preforms, bottles and packages and the specificcompositions of the various layers of such multilayer objects aredisclosed in U.S. Pat. Nos. 4,781,954; 4,863,046; 5,599,496 and6,090,460, the disclosures of all of the foregoing of which areincorporated herein by reference in their entirety.

FIGS. 7A-7D schematically show a typical three-shot multilayer injectionmolding process for forming the five-layer, three-material preform ofFIGS. 5A and 5B. The preform is formed in a mold cavity 466 between anouter mold 300 and core 302 of a conventional injection mold. A firstshot of first polymer material 318 is injected into the lower end (gate)of the mold cavity and as it flows through the mold cavity 466, due tothe relatively cool temperature of the outer mold 300 and core 302,there will be solidification of the first polymer material bothexternally and internally of the mold cavity to define inner 304 andouter 306 layers (layers 132 and 134 in FIG. 5B) of the first material.In FIG. 7A, the first material has progressed part way up the moldcavity walls. As shown in FIG. 7B, a second shot 320 of a second polymermaterial, e.g., a barrier material, is injected into the bottom of themold cavity 15. The relatively small amount of barrier material 320 maypool at the lower end of the cavity. A third shot 322 of a third polymermaterial is then injected into the gate at a pressure which causes thesecond shot material 320 to be pushed up the mold cavity and form innerand outer intermediate layers 309, 310 of the preform (layers 136 and138 in FIG. 5B), while the third material 322 forms a central core layer328 in FIGS. 7C, 7D (layer 130 in FIG. 5B). The tunnel flow of thesecond 320 and third 322 shots between the exterior layers 304 and 306enables the formation of relatively uniform and thin interior layers 309and 310 of the barrier material 320, and a thicker layer of material 322in the core layer 328. Finally, the advancing layers reach the end ofthe mold cavity, producing the five layer preform structure shown inFIG. 7D. Alternatively, the interior layers 309, 310 and 328 may extendonly partially up the preform wall and terminate, for example, below thepreform neck finish 114. This process is described by way of exampleonly, and is not meant to be limiting; many other processes may be usedto form multilayer articles, including articles other than preforms.

FIG. 3 shows part of an injection molding system for carrying out athree shot process, e.g., for making a five-layer article as describedwith reference to FIGS. 7A-7D. The system 4 of FIG. 3 includes a moldcore and cavity set 302, 303, an associated nozzle 468 and actuator 400,a manifold 18, and three separate sources 20, 22, 34 of polymermaterials. For purposes of discussion, only one molding cavity 466 isshown in FIG. 3. A first shot of first (e.g., structural) polymermaterial is fed by a screw/barrel 20 to either a single cavity or toeach of a multiple number of cavities through a common feed manifoldchannel 44. As shown, the common feed channel 44 communicates withindividual feed channel 48 by valve 38. The feed channel 48 communicateswith a central axial bore 460 of nozzle 468 (shown in FIGS. 3 and a morespecific example of a nozzle design in FIGS. 8A-8C). Nozzle bore 460delivers the first shot to gate 464 (FIGS. 8A-8C) which serves as theentrance to cavity 466. An actuator 400 connected to a valve pin 450controls the opening and closing of all of the nozzle bores 458, 460,462 (FIGS. 3 and 8A-8C) according to a predetermined program. Asdescribed in detail below, a predetermined intermediate or end point(conclusion) of the first shot of material is determined as a result ofthe sensing of a property of the amount or flow of the first shot offirst material in or into the mold cavity 466. The actuator 400 is shownonly schematically in FIG. 3. Actuator 400 can be a singlepiston/chamber actuator as shown in the specific embodiment of FIGS.8A-8C, a multiple piston/chamber, or another known actuator designsuitable for use in injection molding valve pin applications.

A second shot of a second selected polymer material, e.g. an oxygenbarrier or scavenging material, is next performed subsequent to thefirst shot. In a single cavity application, the second shot is commencedupon completion of the first shot. In a multiple cavity application, thesecond shot is preferably begun only after the first shot is completedin each/all of the multiplicity of cavities as detected by sensors. In amultiple cavity application the second shot is commonly fed to amultiplicity of cavities by screw/barrel 34 via a common feed manifoldchannel 42 that fills metering pots 29 in the embodiment shown. Thecommon feed channel 42 communicates with individual feed channel 46 viavalve 40. Valve 40 is closed at the start of the second shot (andpreferably at the conclusion of the first shot) to separate and closeoff channel portion 46 and metering pot 29 from communication with therest of the system such that metering pot 29 can separately control thefluid material pressure in the cavity 466 and its associated nozzlechannel 462. In the embodiment shown, metering pots 29 are used todeliver a precise amount of the second material to each cavity 466. Inan alternative embodiment, metering pots 29 can be eliminated anddelivery of the second material can be carried out exclusively viascrew/barrel 34. In the one embodiment shown, the individual feedchannel 46 communicates with a central axial feed bore 460 of nozzle 468that feeds the same gate 464 (FIGS. 8A-8C) and cavity 466 as the firstshot. The metering pots 29 for feeding individual cavities are typicallyarranged and adapted to be mounted on the hotrunner or manifold 18portion of the system 4 such that the individual metering pots 29 can bereadily configured to fluidly communicate with each separate manifoldchannel portion 46 that separately communicates with an individualcavity 466.

In a three-shot, three-material process, a third shot is injectedsubsequent to the second shot. As shown in FIG. 3, the source of thethird feed material 22 is provided with a common machine metering pot56. The common metering pot 56 can be mounted on the injection moldmachine itself (as opposed to the manifold 18) for purposes of acting asa source of stored and ready material for simultaneous feed to all of amultiplicity of cavities. Such a stored intermediate volume of materialas in pot 56 is typically employed to ensure that a sufficient amount ofmaterial is available in the system for injection during the course ofan injection cycle that is relatively short in time duration, i.e. dueto the shortness in time duration of a cycle, a machine screw/barrel maynot be able to produce sufficient molten polymer material; the pot 56thus acts as an internal reservoir of material ready to replenish thesystem for the next cycle. In the embodiment shown in FIG. 3, themachine metering pot 56 is fluidly connected to the screw/barrel 22 forinjecting the selected third material as a third shot (FIGS. 7C, 7D). Ascan be readily imagined such a machine metering pot could alternativelyalso be provided in connection with the operation of feed barrels 20,34.

In the embodiment shown in FIG. 3 (and FIGS. 8A-8C), the third shot isdelivered to cavity 466 through the same gate 464 via a third bore 458provided in the nozzle 468. In a single cavity application, the thirdshot is delivered subsequent to completion of the second shot. In amulti-cavity application, the third shot is preferably begun to allcavities after all of the metering pots 29 to all of the multiplecavities have discharged/injected their contents to the individual feedchannels 46. Alternatively, the third shot can be commenced at theconclusion of a predetermined amount of time in which it is assumed thatthe second shot has been completed to all cavities. Prior to the startof the third shot, the machine metering pot 56 is filled and the valve62 closed. Valve 63 is then opened to commence the third shot to allcavities. The common manifold channel portion 58 communicates with andallows simultaneous injection to all of the multiplicity of cavities.The purpose of the machine metering pot 56 is to ensure that an excessof fluid material is always present in the system between thescrew/barrel 22 and the cavities and ready for injection from oneinjection cycle to the next.

Each of the multiplicity of cavities communicates with the commonmanifold channel 58 via a separate or individual manifold channelportion such as channel portion 60 that communicates with the thirdseparate bore 458 in the nozzle 468. Bore 458, like the other nozzlebores, communicates with the gate 464 of cavity 466. The third separatebore 458 is radially offset from the central axial bore 460 butterminates at and feeds the gate 464 to the cavity 466.

In a multilayer process where the first shot comprises a structuralpolymer material and the second shot comprises an oxygenscavenging/barrier material, it is particularly desirable to ensure thatthe first shot of material is uniform in volume among all of themultiplicity of cavities. As shown in FIG. 4, the amount of materialthat fills two different cavities can vary over the course of the cycletime of the first shot. As illustrated in FIG. 4 (starting on theleft-hand side), shortly after the valve gates are open, the first shotinitially fills one cavity (cavity 2) at a slower rate than anotheridentical cavity (cavity 1) due to differences in the channel or nozzleor cavity size, or in the temperature of the manifold channels, thenozzle or the mold bodies associated with the two identical cavities.The object in such a multilayer or multimaterial injection process is toachieve identical or as close to identical fill volumes as possible ineach cavity of a multi-cavity system in the first shot of material.

The desired end result of equalization illustrated (on the right-handside of FIG. 4) can be achieved according to this embodiment of theinvention by separately controlling the fill volume and/or rate of eachindividual cavity using separate valves for each cavity that arecontrolled by a controller that senses when each cavity has reached acertain fill volume or otherwise determines the fill/flow rate. Suchcontrol over the fill of individual cavities can be effected bymonitoring a property of either the material flowing into eachindividual cavity or by monitoring a property within each individualcavity or the nozzle or mold body associated with each individual cavitythat is indicative of the flow rate or the actual volume of materialflowing into or that has flowed into each individual cavity at any givenpoint in time during the injection cycle. The monitored or sensedproperty can then be used as a factor for determining when the moldcavity has reached a predetermined fill volume. Once such adetermination is made, the injection process for the first shot ofmaterial can be continued for certain period of time, or stopped, whenthe property being sensed has reached a predetermined value. As shownschematically in FIG. 2, each separate cavity or the mold body or thenozzles or a portion of the manifold associated with each separatecavity has at least one associated sensor S1, S2, S3, S4 that senses andgenerates a signal indicative of the rate of flow or volume of materialflowing to or into each cavity.

In one embodiment, the sensors S1-54 are interconnected to a controller(e.g., microprocessor or computer) 28 that is, in turn, interconnectedto a multiplicity of valves 24 a, 24 b, 24 c, 24 d that control the feedof a pneumatic or hydraulic drive fluid to and from a multiplicity ofactuators 26 a, 26 b, 26 c, 26 d that drive valve pins 27 a-27 d. As canbe readily imagined a single sensor or a single set of sensors can beemployed in connection with a single cavity such that the controller 28controls delivery to the single cavity. In the embodiments shown anddescribed, multiple cavities are controlled simultaneously. As describedin detail below the actuators 26 a-26 d control the axial positioning ofthe valve pins 27 a-27 d within a plurality of injection nozzles, suchas nozzle 468 of FIG. 3. Depending on the precise axial position of thepins 27 a-27 d within the nozzles, the operation of which are controlledby controller 28, the flow of the first, second and third polymermaterials can be modified, stopped or started at any selected point inany given injection cycle.

Alternatively, the operation of the actuators can be controlled byinterconnecting the controller 28 to the drive control mechanisms thatoperate the pumps or other sources of drive fluid 20, 22 that are fed tothe actuators 26 a-26 d (FIG. 2). The controller 28 includes a programthat receives the property indicative signals from each sensor S1-S4 (oranother signal resulting from receipt and/or processing of the sensorsignals) and uses the signals as a variable for controlling movement ofthe valve pins 27 a-27 d in the manner described above. The controller28 can control operation of either the drive sources 20, 22 for pumpingfluid to the actuators or by controlling operation of the valves 24 a-24d that enable drive fluid to flow to the actuators 26 a-26 d, or bycontrolling both. The controller 28 typically comprises a digitalprocessor and associated memory. The controller 28 can take the form ofa computer, a microprocessor or any other conventionally known digitalelectronic processing and storage mechanism. The controller 28 cancomprise a unitary processing mechanism and/or associated memory or aplurality of such mechanisms that communicate and cooperate with eachother to coordinate and achieve control over the drive elements that areresponsible for the precisely timed operation of the various componentsof the injection mold apparatus such as the actuators, manifold andmachine valves, the machine screw/barrel, the metering pots and allassociated valves.

FIGS. 8A, 8B and 8C show one example of a nozzle design for deliveringselected amounts of three materials in three successive shots to acavity at predetermined times during the course of a single injectioncycle. As shown, the actuator system comprises a single piston actuator400 having a piston 412 sealably mounted within a chamber 414 forreciprocal fluid driven movement (hydraulic or pneumatic) of the piston412 and any associated/attached parts such as valve pin 450 along axis Xof mold chamber 466. In the manner described above with reference toFIG. 2, controller 28 directs the drive of piston 412 according to aprogram that receives and uses a signal received from a sensor Sassociated with a mold cavity 466 or nozzle 468 or their associated moldor manifold bodies. For purposes of discussion, S is intended togenerically indicate one or more sensors located at any preselectedposition within the system sensing any preselected property(ies) ofpolymer material in the mold body such as temperature, pressure, flowrate or an optical property. In a multi-cavity system according to theinvention, the controller 28 receives multiple signals from amultiplicity of such sensors S that are individually associated withseparate mold cavities (which, in turn, are associated with separatenozzles 468 and actuator/pin assemblies) such that the controller 28 issimultaneously directing the drive of a multiplicity of actuatorassemblies in a multi-cavity system during a single injection cycle andparticularly during the period of time when the first shot is beingdelivered.

FIG. 8A shows the start position of the actuator 400 and the valve pin450 in a typical three material shot injection cycle. In the closedposition of FIG. 8A, all three material flow channels 458, 460 and 462are closed such that there is no flow of any of the three materials intoor through the gate passage 464 to the cavity 466. FIG. 8A also depictsthe position of the actuator 400 and pin 450 at the conclusion of thefirst shot and at the conclusion of the entire injection cycle of allthree shots.

FIG. 8B shows a second position of the valve pin 450 in which the pin isretracted from the start 8A position such that the first shot is readyfor delivery. In the FIG. 8B position all of the nozzle bores 458, 460and 462 are open. As described with reference to FIG. 3, the first shotof virgin material is delivered from the injection screw/barrel 20through nozzle bore 460 in the nozzle 468. Upon movement of the pin 450to the FIG. 8B position, flow of the first shot of first materialcommences. Once the first shot is underway, cavity 466 begins to fill inmanner and profile as shown schematically in FIG. 7A. When the sensor Ssenses a predetermined value for a preselected property such as thepressure or temperature of the first material within the nozzle bore 460(e.g. via sensor S9) or within the cavity 466 (e.g. via sensor S5 orS6), the sensed property signal is sent to and received by controller 28and a value indicative of the sensed and received property signal isused in a predetermined program executable by the controller 28 todetermine precisely when the pin 450 should be moved back to the closedposition of FIG. 8A (and/or when manifold channel valve 38 (FIG. 3)should be closed) to stop the flow of the first material through channel48 and nozzle bore 460.

For example, the sensor S5 or S6 or S9 can comprise a pressuretransducer that sends a signal indicative of material pressure in moldcavity 466 or channel 460 to the controller 28. In one typicalembodiment, the controller 28 program can include instructions thatorder actuator 400 to move pin 450 to the FIG. 8A position uponcalculating the fill volume, e.g., based upon receipt of a signal from asensor that indicates that the material pressure has reached apredetermined value at a predetermined time at a preselected locationwithin cavity 466 (e.g. at a 20% fill position). Alternatively, theprogram could determine when fill of the first shot is complete bycalculating flow rate and/or volume of flow into the cavity 466 based onthe measured pressure of the material over a measured period of time bya sensor such as S9 or S5 or S6. Alternatively, the program can includeinstructions that order actuator 400 to move in response to receipt of apredetermined value of a signal from a sensor S10 that monitors thepressure of the drive fluid in actuator chamber 414. The drive fluidpressure is indicative of the material pressure being exerted on pin450. Another example of a program is one that utilizes the time lapse orinterval between receipt of signals from sensors S5 and S6 which mightsense a property of the material within cavity 466 at the locationsshown in FIG. 7 a, the property sensed being a property such astemperature, pressure or an optical property. The program might then usesuch a sensed time interval or lapse to calculate the rate of flow ofmaterial within cavity 466 and utilize such a value to instruct thevalve pin 450 to move to the position shown in FIG. 8A.

The precise algorithm or program used by the controller 28 to controlthe position of the pin 450 or the closing of valve 40 can be any of awide variety of algorithms/programs depending on the choice of theprogrammer/designer of the system and depending particularly on thechoice and location of sensors (pressure, temperature, optical and thelike). Whatever the precise algorithm/program that is selected forcontrolling the start, adjustment and/or stoppage of material flow ofthe first material, the algorithm/program is designed to preciselycontrol delivery of the first material to the cavity(ies) in order toachieve delivery of a precisely predetermined volume of the firstmaterial, e.g., the same precisely predetermined volume to any oneindividual cavity from one injection cycle to the next, and/or todeliver the same precisely predetermined volume of material to each andevery one of a multitude of cavities in a multi-cavity application.

Thus, the use of such programmed control of a valve to individuallycontrol the volume of fill of the first shot can be employed toconsistently obtain the same volume of fill for a single cavity betweensuccessive co-injection cycles. The use of such programmed control canalso be used to obtain an equal or uniform volume of first shot fillamong a multiplicity/plurality of cavities in a multi-cavityapplication.

As with screw/barrel 22 which feeds the third shot of material, thefirst shot screw/barrel 20 can be provided with a machine pot (notshown) in an arrangement similar to the arrangement of machine pot 56relative to screw/barrel 22. However, the use of individual manifoldmetering pots (similar to 29 used for the second shot) is eliminated forthe first shot because controller 28 and sensor S monitor and controlcompletion of the necessary volume of material to cavity 466.

As noted with reference to FIGS. 1 and 4, the rate of fill of theindividual cavities in a multi-cavity system can and will vary. In amost preferred embodiment, the program of the controller 28 includesinstructions for delaying the start of delivery of the second shot ofthe second material to all cavities of a multi-cavity system until theprogram of the controller 28 determines, based on use of receivedsignals from all relevant sensors at all cavities, that delivery of thefirst shot has been completed to all of the multiplicity of cavities. Insuch an embodiment, immediately upon determination by controller 28 thatthe first shot has been completed in all cavities, the controller 28directs the valve pin 450 to return all bores to the closed position ofFIG. 8A. The controller 28 then directs the valve pin 450 to move to theposition shown in FIG. 8C where bore 462 is open and bores 458, 460 areclosed (for delivery of the second shot). In an embodiment wheremanifold metering pots are employed, controller 28 directs the drivemechanism(s) for metering pots 29 associated with each individual cavity466 to begin injection of the second shot of the second polymer materialthrough each individual manifold channel portion 46 and through eachindividual second shot nozzle bore 462 and through each individual gate464 into each individual cavity 466 to achieve the second shot fillprofile shown in FIG. 7B.

Most preferably, the second shot of the second material (preferably arelatively small amount of an oxygen scavenging or barrier material,typically less than about 10% by weight of the first shot of material)is delivered by use of a metering pot 29. As noted previously, the useof an individual metering pot 29 can be eliminated. In an embodimentthat does not use a metering pot, controller 28 can be interconnected tothe drive mechanisms for valve 40 and/or screw/barrel 34 so as to directoperation of these components to stop delivery or flow of the secondmaterial to the cavity after the elapse of an empirically determinedamount of time (when it is known that a sufficient amount of the secondmaterial has been delivered to either a single cavity in single cavityapplication or to all of a multitude of cavities in a multiple cavityapplication).

In a multi-cavity application where a third shot is deliveredsimultaneously to all cavities via a common manifold channel 58 (seeFIG. 3), the third shot is preferably commenced upon completion of thesecond shot in/to all of the multitude of cavities. At the conclusion ofthe second shot, the valve pin 450 is in the position shown in FIG. 8C.As shown in FIG. 8B, when the pin 450 is further retracted to the FIG.8B position, the terminal end of the third shot nozzle bore 458 is influid communication with the gate 464 and cavity 466. In an embodimentwhere a metering pot is used for delivery of the second shot, conclusionof the second shot can be determined by monitoring the point of fulldischarge of all metering pots 29 associated with all cavities. Analternative method is to separately begin delivery of the third shot ateach individual cavity immediately upon determining that any individualmetering pot 29 has been discharged. FIGS. 7C and 7D show a typical flowpattern and profile for delivery of the third shot of the third materialover the course of the cycle of the third shot.

The program of the controller 28 can include instructions that processor otherwise utilize any one or more of a variety of property valuessensed by appropriate sensors. For example, temperature, pressure or anoptical property alone can be used as the sole signal sent to thecontroller and a variable indicative of such signal can be input to theprogram to determine the end point of the first shot. As shown in FIGS.2 and 8A-8C sensors can be mounted to detect and sense a property of thematerial flowing in any one or more of a variety of different locations:S5 and S6 sensing material in a mold cavity, 39 sensing material innozzle bore 460, and S10 sensing a property such as pressure of thedrive fluid for the actuator 400.

The controller program or algorithm can utilize sensor signalspertaining to flow rate as the basis on which the end point of the firstshot is determined to occur. Flow rate can be determined, for example,by the difference in time between which two sensors, e.g. S5 and S6sense a pressure or temperature or optical property of the materialflowing within a cavity 466. As shown, the sensors S5 and S6 arestrategically located in different locations along the flow path withinthe cavity, S5 being upstream of S6. Successively located sensors suchas S5 and S6 could alternatively be mounted to sense material flowwithin a nozzle bore or a manifold channel, in the same manner as sensorS9 senses a material property within bore 460.

Where a property such as pressure or temperature or flow rate is used bya program to determine the precise timing of the sending of aninstruction to an operational component of the injection mold apparatus,it is preferable to initially conduct a series of trial and error runsof shots of first, second and/or third materials to empiricallydetermine a profile of the selected sensed property over a cycle thatproduces the most satisfactory end product. Such an empiricallydetermined ideal profile of material pressure, temperature or otherselected property that exists at any given/selected sensor locationduring the conduct of such a trial run can be saved as a set of targetprofile data which the program can then use to compare against signalsreceived from sensors during actual manufacturing cycles. When theprogram determines a match between the sensor signals received during anactual manufacturing run with the target and data stored in thecontroller 28 (e.g. material pressure in the cavity), the program canthen, for example, determine that injection is complete or will becomplete after a known period of time in a given cavity and instruct thevalve 38 or actuator 400 (FIG. 3) to move to a closed position and thusterminate the first shot injection of first material.

These and other modifications would be readily apparent to the skilledperson as included within the scope of the described invention.

1-22. (canceled)
 23. A method of delivering multiple shots of materialto a plurality of mold cavities, the method comprising: for each of theplurality of mold cavities, providing sensors at two locations of flowin or into the cavity; delivering a first shot of a first materialsimultaneously to the plurality of mold cavities; independently sensingfor each cavity at the two locations a property that is indicative of avolume or flow of the first material in or into the correspondingcavity; independently stopping the step of delivering the first shot toone or more cavities according to a program that uses as a variable asignal indicative of the property sensed at the two locations for thecorresponding cavity during delivery of the first shot to estimate whenthe mold cavity will or has reached a predetermined fill volume, whereinthe program uses the signal indicative of the sensed property at the twolocations to calculate a flow rate or fill volume of the first materialor to compare the signal or a value calculated from the signal to atarget value; and delivering a second shot of a second materialsimultaneously to the cavities subsequent to the step of stopping thestep of delivering the first shot.
 24. The method of claim 1 whereineach cavity has a corresponding nozzle fluidly communicating with thecavity and having a first bore for delivery of the first shot, thenozzle having a valve pin adapted to open and close the first bore, andthe step of independently stopping the first shot comprising closing thefirst bore.
 25. The method of claim 1 wherein the step of delivering thesecond shot comprises delivering the second shot subsequent to stoppingdelivery of the first shot to all of the plurality of cavities.
 26. Themethod of claim 1 wherein the step of delivering the first shotcomprises delivering the first material to all of the plurality ofcavities from a single source of injection.
 27. The method of claim 1wherein the step of delivering the second shot comprises delivering thesecond material to each cavity from a separate source of injection. 28.The method of claim 1 wherein the step of independently sensingcomprises sensing a volume of the first material.
 29. The method ofclaim 1 wherein the step of independently sensing comprises sensing aflow of the first material.
 30. The method of claim 24 wherein eachnozzle has first and second bores for delivering the first and secondmaterials respectively to the corresponding cavity, the valve pinreciprocating between positions to open and close the first and secondbores, and the program including instructions to direct the valve pin tomove between the positions to fill the cavity to a predetermined volumeof the first material.
 31. The method of claim 24 wherein the twolocations are within the bore of the nozzle or within the correspondingcavity.
 32. The method of claim 1 wherein the program calculates theflow rate of the first material.
 33. The method of claim 1 wherein theprogram calculates the fill volume of the first material.
 34. The methodof claim 24 wherein the nozzle communicates with sources of pressurizedfeed of the first and second materials; a drive mechanism drives one orthe other or both of the sources of feed and the valve pin for thenozzle, the drive mechanism starting and stopping flow of each of thefirst and second materials in a predetermined sequence through thenozzle; a controller, interconnected to the drive mechanism, receivingone or more signals from the two sensors and directing the drivemechanism to deliver at least the first shot of the first material andthe second shot of the second material after the first shot.